This invention relates to an apparatus and method for folding sheet materials such as plastic film of the type used, for example, to manufacture packaging materials and the like.
In the manufacture of polyethylene bags, it is conventional to fold the sheet material widthwise. This may be done as the material is extruded, or the material may be first stored in large rolls and then folded. In what is believed to be the most widely used commercial folding process, the unfolded film is shaped around a triangular form and the folded film removed continuously from the apex of the triangle at right angles to the direction of feed. See U.S. Pat. Nos. 229,479 of Scholfield and 4,285,686 of Ambler. When folding stretchable plastic materials (such as polyethylene), this process leads to excessive waste because of undesired stretching of the film as it is removed from the apex of the triangular form.
Long tubes of sheets folded in this manner may be heat-sealed from edge to edge at longitudinally-spaced-apart intervals and then cut just above or below the seals to form simple bags without gussets and with minimally reinforced bottoms. Preferably, however, the sheets are folded again one or more times in the same manner in order to provide bags that have a more complicated but stronger construction.
In order to reduce the waste, which is particularly significant in cases where the plastic sheet material is being folded as it comes from an extrusion machine, the assignee of the present invention developed and used a folding apparatus comprising forming blades, which are universally adjustable, in conjunction with a deflection bar which enables the geometry of the device to be adjusted in such a way that films of variable width can be folded continuously and with substantially reduced waste as compared to the above-described process in which a triangular form is employed. The use of these forming blades and deflection bar, however, requires a fairly sophisticated adjustment procedure to accommodate sheeting materials of different widths. If well-trained labor is not available, the need to adjust the blades and deflection bar can result in excessive waste where the apparatus is used in conjunction with an extrusion device or the like wherein the plastic material is continuously supplied to the folding apparatus.